Commutated transformer



May 20, 1947. K. 1.. HANSEN 2,420,950

COMMUTATED TRANSFORMER Original Filed Aug. 21, 1944 INVENTOR. rfuw Z.Mwm

Y QJM 444 v5 Patented May 20, 1947 COMMUTATED TRANSFORMER Klaus L.Hansen, Milwaukee, Wis.

Original application August 21, 1944, Serial No. 550,429. Divided andthis application July 13, 1945, Serial No. 604,773

Claims.

This invention relates to a dynamo-electric machine.

This application is a division of my copending application Serial No.550,429 filed August 21, 1944, for Rectifier and transformer unit, nowPatent No. 2,415,007 dated January 28, 1947.

Objects of this invention are to provide a combined transformer anddynamo-electric machine which isso made that the device has two mainelements constituting a rotor and a stator respectively, one of theelements being a transformer element and having polyphase primary andsecondary windings, and the other main element having a direct currentWinding and a shortcuited winding, the element which constitutes therotor driving the commutating means.

In commutation, particularly polyphase commutation, harmonics areusually produced due to the fact that commutation often occurs at pointsdifferent from the zero points of the alternating current. Theseharmonics, if the device were used as an inverter to convert directcurrent into alternating current and if no provision were made to takecare of them, would be passed from the primary through the secondary outon the line and would give trouble, particularly if the line were a highimpedance line, as they would cause a loss of energy and would beradiated from the line thus producing inter-ference with communicationsystems.

Further objects are to provide, in a device of the above defined type, ashort-circuited tertiary winding closely interlinked with the primarywinding of the transformer and rotated synchronously with thefundamental frequency for which the device is designed.

It has been found that the short-cirouited tertiary winding, which isclosely interlinked with the primary winding through which the harmonicspass, offers a low impedance path for the harmonics and produces amagnetic flux in opposition to that produced by the harmonics andprevents generation of high voltage due to the harmonics and preventspassage of the harmonics through the transformer unit onto the line andprevents any material waste of energy due to the harmonics. In additionto this it has been found that commutation is also greatly improved.

Further objects of this invention are, therefore, to provide a combineddynamo-electric machine and transformer unit which is so made thatharmonics generated due to the action of the commutating means find alow impedance path through the primary windings due to the coaction ofthe short-circuited tertiary winding with the primary windings of thetransformer and are, therefore, prevented from being sent out on theline, and to so arrange the tertiary circuit that it is rotated insynchronism with the fundamental frequency and does not waste any energydue to the fundamental frequency.

Further objects are to provide a combined polyphase dynamo-electricmachine and transformer which is so made that commutation takes placefor each phase and the output from all of the phases is added in thedirect current circuit, in which, when the current flow is reversed withreference to any given primary, a by-pass circuit is formed around suchprimary to prevent an instantaneous dip or dropping or variation in thedirect current due to the reactance of such primary, the arrangementbeing such that no primary acts as a choke.

In greater detail, further objects are to provide a combined polyphasedynamo-electric machine and transformer which is so made that during theperiod of commutation for any given phase a variable resistance isinserted in the bypass circuit around the primary just prior to theinstant of rectification, in which this resistance is decreased to anapproximate zero value at the instant of commutation and is againinserted in the by-pass, circuit just after commutation, and in whichthe by-pass circuit is either finally opened or else its resistance verygreatly increased, the complete opening of the by-pass circuit at thisinstant being the preferred construction.

Further objects are to provide a device of the above outlined characterwhich may be used, if desired, as an inverter to change direct currentto alternating current, or which may be used as a direct current motordriving a mechanical load in which case the secondary would either beleft open or wholly omitted.

Further general objects of this invention are to improve commutation.

Further objects are to provide a dynamo-electric machine which isefficient, which is selfstarting, and which, though having the desirablecharacteristics set forth above, is of simple construction.

An embodiment of the invention is shown in the accompanying drawings, inwhich:

Figure 1 is a schematic view showing the dynamo-electric machine.

Figure 2 is a fragmentary view, partly broken away, showing a portion ofthe stator and rotor with one of the end rings sectioned off.

The device will be described in detail as an inverter for convertingdirect current into alternating current, thouh it is to be understoodthat the device may be used as a motor driving a mechanical load.

The device comprises a synchronous motor structure in which the two mainelements constituting the stator and the rotor are arranged torespectively provide a transformer unit having primary and secondarywindings and a second unit having a direct current winding and ashort-circuited winding. The invention has been shown with thetransformer unit forming the stator unit and the direct current andshortcircuited windings carried by the rotor unit, though thisarrangement, of course, could be reversed.

Referring to the drawings, it will be seen that the stator is providedwith a polyphase secondary winding indicated by the reference characterI, which may be a three phase winding provided with taps. A polyphaseprimary winding 2 is provided. For simplicity it may be a two phasewinding as shown.

The rotor is provided with a direct current winding 3 which i adapted toproduce the poles of the rotor. The rotor carries a short-circuited.winding which may be in the form of a squirrel cage, the bars beingindicated by the reference character 4 and the end rings by thereference character a. This short-circuited Windin constitutes atertiary winding which, as will be seen as the description proceeds,insures a low impedance path for harmonics, prevents their passage outonto the line, prevents any material energy loss due to such harmonicsand does not absorb energy at the fundamental frequency for which thedevice is designed and operated. In the schematic showing in thedrawings the rotor has been shown as a two-pole rotor, though, ofcourse, the stator and rotor could be formed so as to provide four polesor any number of poles desired, corresponding changes being made in thenumber of commutation segments and brushes in the commutating portion ofthe apparatus. rotor shaft also carries two commutators indicatedgenerally by the reference characters 6 and 1 each having a pair ofsegments, indicated at 6 and 6" and l" and '1, respectively. Thesesegments are arranged at right angles to each other. A pair of brushes 8bear upon the cornmutator 6 and are connected to opposite sides of oneof the two phase primary windings 2. Similarly a pair of brushes 9 bearon the commutator 7 and are connected to opposite ends of the other ofthe two phase primary windings 2. The segments 1 and 6" are directlyelectrically connected. The rotor shaft also carries a pair of sliprings l and H which are connected respectively to the segments 8 and l".Brushes l2 bear on the slip rings and are connected to the source ofdirect current l3 when the device is used as an inverter to convertdirect current into alternating current or when the device is used as adirect current motor for driving a mechanical load.

It is preferable to have the short-circuited winding consisting of thebars 4 and the end rings closely coupled with the primary 2. This isreadily accomplished by winding the secondary windings l in the outerportions of slots in the stator and winding the primary windings 2 inthe inner portions of the slots of the stator. Obviously the primary andsecondary windings may be distributed windings or may be formed in Theany other way desired and may be of the same or of a different number ofphases.

By shifting the taps on the secondary any desired alternatin currentvoltage may be obtained when the device is used to convert directcurrent into alternating current.

It is to be noted that there is a very close inter-linking of theprimary Winding 2 and the short-circuited tertiary winding of the rotor.Consequently harmonics produced by the dynamo-electric machine will beprevented from being transmitted back out onto the line as theshortcircuited winding or tertiary winding causes a low impedance pathto be offered to these har monies and at the same time since theshortcircuited winding rotates synchronously with reference to thefundamental frequency for which the device is designed, it is apparentthat the short-circuited winding will absorb no energy due to thattransmitted at the fundamental frequency.

Both the short-circuited tertiary Winding and the commutating bridgingmeans hereinafter described in detail coact to improve commutation. Itis, of course, within the province of this invention, even in thepreferred form, to omit the short-circuited tertiary winding. In thiscase the entire reliance for excellent commutation would be placed onthe short-circuited commutating means.

The preferred form of construction has been illustrated in that thestator is preferably the transformer unit and the rotor preferablycarries the short-circuited winding and the direct current winding,though, as stated, these two main units could be reversed.

The commutators 6 and "I may not interrupt the circuit at exactly thezero point and consequently there is a very pronounced tendency toproduce harmonics differing, of course, from the fundamental frequency,but inasmuch as this invention provides means whereby a low impedancepath is furnished such harmonics, obviously such harmonics do not wasteany material portion of the energy supplied the machine and also are notpassed out onto the alternating current line when the device is used asan inverter. It is believed that the above points will be betterunderstood when it is considered that at the instant the commutator I iscommutating, it is also reversing the current flow through itscorresponding primary coil, and, similarly, when the commutator 6 iscommutating, it is also reversing the current flow through itscorresponding primary coil. It is clear that by providing theshort-circuited tertiary winding, this reversal of current is greatlyfacilitated and commutation is very much improved.

This invention provides means whereby the reversal of current through aparticular primary winding of the transformer does not have to suddenlyoccur. Instead, this invention provides a by-pass short-circuiting patharound that particular primary at the instant of commutation for suchprimary and into this path a variable resistance is interposed justprior to commutation, is reduced to an approximate zero value at theinstant of commutation, and is increased just after commutation untilthat particular primary is in condition, due to its normal transformeraction, to take its share of the load. This arrangement thus preventsany primary winding from acting as a choke, the arrangement being such,as will be seen as the description proceeds, that the insertedresistance is confined to the by-pass path and does not increase theresistance in the circuit through the primaries 2, as it is in parallelwith that particular primary during commutation.

The immediately above described desirable features are accomplished byadding the commutator indicated generally at 14 to the shaft driven fromthe rotor. This commutator comprises a plurality of segments which arearranged in four groups with all of the Segments of a group connected toa common conductor 15. The centrally located segment of a group isdirectly connected to the conductor It. The next adjacent segments oneach side thereof are connected to the conductor I 6 by small value,high current capacity resistors H and the next adjacent segments on eachside are connected to the conductor It by resistors I8 of higherresistance than the resistors l1 and of high current capacity.

Any number of gradually increasing resistors can be employed. Preferablyan idle segment it is interposed between each group of segments, though,of course, it is Within the province of this invention to connect onegroup of segments to a succeeding group of segments by a relatively highresistor if so desired. The conductors G6 are connected in a regularorder to the segments 6, 6" of the commutator S and l, 1" of thecommutator l. Short-circuiting brushes 2!) are 'directly connected bymeans of the conductor 2i and bear on diametrically opposed groups ofthe segments, it being noted that the diametrically opposed groups ofthe segments for a two-pole rotor as indicated are connected to thesegments of the same commutator, for instance the commutator 6, andthose at right angles thereto are connected to the segments of the othercommutator, for instance the commutator I.

At the instant that the parts are in the position shown in Figure 1, itis apparent that one phase of the primary windings 2 is supplied withcurrent while the other primary is passing through its zero point andcommutation is taking place just at the instant that the reversal ofcurrent flow in such other primary winding is about to take place. Inorder to prevent any choking action of the primary winding then beingcommutated, a direct short-circuit path or by-pass path is formed aroundsuch primary winding and the current flows through this short-circuitingbypass path, thus preventing the reactance of the primary winding thenbeing commutated from adversely affecting the current flow.

As the commutator I4 rotates, a relatively small value, high capacityresistor is inserted into this by-pass circuit and the resistance of theby-pass circuit is gradually and automatically built up until finally itarrives at an infinite value as such by-pass circuit is opened in theform of the invention shown, thus allowing the last mentioned primarywinding to assume its share of the current. The current in the primarycircuit, therefore, never drops to zero. It is also to be noted thatjust prior to commutation for any primary resistances of succeedinglydecreasing values are inserted in the by-pass circuit to thus provide aby-pass circuit for the decreasing current flow taking place in thatparticular primary due to the normal transformer action.

In addition to this, the tertiary circuit, namely, the short-circuitedbars on the rotor, prevents the passage of any harmonics out onto thealternating current line.

It is to be understood that the device can be operated to convert directcurrent into alternating current by supplying direct current to thebrushes l2 from the source l3 as has been described in detail. Also thedevice can be run as a direct current motor in which case the secondarywould either be left open or wholly omitted.

When the apparatus is run in the capacity of an inverter, it is to benoted that the amount of energy required by the synchronous motor unitis relatively small in proportion to the amount of energy which istransmitted to the alternating current circuit and consequently theeiliciency of the apparatus is high.

It will be seen also that in view of the fact that a rotating field isproduced, the device constitutes a self-starting dynamo-electricmachine.

It will be seen further that this invention provides a dynamo-electricmachine which does not waste any material amount of energy due toharmonics and prevents the harmonics from being passed onto thealternating current line and prevents the primary windings from actingas chokes during commutation when the current flow therethrough isreversed and in which an average value of direct current is drawn fromthe direct current source without allowing the direct current to drop tozero value at any portion of the commutation cycle.

It is within the province of this invention to provide a construction inwhich a single phase secondary is used and a polyphase primary in thetransformer element of the unit. Under these conditions the motor wouldrun as a direct current motor and polyphase current would be generatedin the primary of the transformer element and single phase current wouldbe generated in the secondary.

Although this invention has been described in considerable detail, it isto be understood that such description is intended as illustrativerather than limiting, as the invention may be variously embodied and isto be interpreted as claimed.

I claim:

1. A dynamo-electric machine comprising a plurality of windings bearinga polyphase relation to each other, a rotor having a direct currentwinding, a plurality of slip rings driven from said rotor, brushesbearing on said slip rings, a plurality of commutators driven from saidrotor and connected in series between said slip rings and connected tothe direct current windin of said IOtOL'bIUShBS bearing on saidcommutators and connected to said windings, and means for establishing aconductive by-pass circuit around each of said windings duringcommutation with respect to such winding,

2. A dynamo-electric machine comprising a plurality of windings bearinga polyphase relation to each other, a rotor having a short-circuitedwinding and having a direct current winding, a plurality of slip ringsdriven from said rotor, brushes bearing on said slip rings, a pluralityof commutators driven from said rotor and connected in series betweensaid slip rings and connected to the direct current winding of saidrotor, brushes bearing on said commutators and connected to saidwindings, and means for establishing a conductive by-pass circuit aroundeach of said windings during commutation with respect to such winding.

3. A dynamo-electric machine comprising a stator constituting apolyphase transformer element and having a plurality of primary andsecondary windings associated in transformer relation, a rotor having adirect current Winding, a

plurality of slip rings driven from said rotor, brushes bearing on saidslip rings, a plurality of commutators driven from said rotor andconnected in series between said slip rings and connected to the directcurrent winding of said rotor, brushes bearing on said commutators andconnected to said primary windings, and means for establishing aconductive by-pass circuit around each of said primary windings duringcommutation with respect to such primary winding.

4. A dynamo-electric machine comprising a stator constituting apolyphase transformer element and having a plurality of primary andsecondary windings associated in transformer relation, a rotor having adirect current winding, a plurality of slip rings driven from saidrotor, brushes bearing on said slip rings, a plurality of commutatorsdriven from said rotor and connected in series between said slip ringsand con nected to the direct current winding of said rotor, brushesbearing on said commutators and connected to said primary windings, andmeans for establishing a conductive by-pass circuit around each of saidprimary windings during commutation with respect to such primary windingand varying the resistance of said by-pass circuit from a predeterminedvalue just prior to commutation, to a minimum value at the instant ofcommutation, and increasing the resistance of the by-pass circuit justafter commutation.

5. A dynamo-electric machine comprising a plurality of windings bearinga polyphase relation to each other, a rotor having a short-circuitedwinding, a plurality of slip rings driven from said rotor, brushesbearing on said slip rings, a plurality of commutators driven from saidrotor and connected in series between said slip rings, brushes bearingon said commutators and connected to said windings, and means forestablishing a conductive by-pass circuit around each of said windingsduring commutation with respect to such winding.

KLAUS L. HANSEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS 1,659,110 Lennox Feb. 14, 1923

